Liquid crystal device

ABSTRACT

Provided are a liquid crystal device, a composition capable of forming a liquid crystal layer, a method of manufacturing the liquid crystal device, a system for manufacturing the liquid crystal device, and a use of the liquid crystal device. The liquid crystal device is a device capable of exhibiting, for example, a normally white or black mode, exhibiting a high contrast ratio, driven with a low driving voltage, and exhibiting excellent durability such as thermal stability. Such a liquid crystal device may be applied to various optical modulators such as a smart window, a window protective film, a flexible display device, an active retarder for displaying 3D images, or a viewing angle control film.

FIELD

The present application relates to a liquid crystal device, apolymerizable composition, a method of manufacturing a liquid crystaldevice, a system for manufacturing the liquid crystal device, and a useof the liquid crystal device.

BACKGROUND

A liquid crystal display (LCD) embodies an image by orientationallyordering a nematic or smectic liquid crystal compound and switching analigning property through voltage supply. A process of manufacturing anLCD is a high-cost process requiring a complicated process, and needs alarge-scale production line and equipment.

A so-called polymer dispersed liquid crystal (PDLC; the term “PDLC” usedherein is a super ordinate concept including a so-called polymer networkliquid crystal (PNLC) or polymer stabilized liquid crystal (PSLC))device embodied by dispersing liquid crystals in a polymer matrix hasbeen known. The PDLC can be manufactured through coating of a liquidcrystal solution, and thus can be manufactured by a simpler process thanthat for a conventional LCD.

As described in the patent document 1, a normal liquid crystal compoundis present without aligned in a PDLC. Accordingly, the PDLC is opaque,which is a non-transparent state, when a voltage is not applied, andsuch a state is called a dispersing mode. When the voltage is applied tothe PDLC, the liquid crystal compound is ordered according thereto tobecome a transparent state, and thus switching between transparent anddispersing modes is possibly performed.

PRIOR ART DOCUMENT Patent Document (PATENT DOCUMENT 1) Korean UnexaminedPatent Application Publication No. 1993-0013794 DETAILED DESCRIPTIONObject

The present application provides a liquid crystal device, apolymerizable composition, a method of manufacturing the liquid crystaldevice, a system for manufacturing the liquid crystal device, and a useof the liquid crystal device.

Solution

One aspect of the present application provides a liquid crystal deviceincluding an alignable polymer network and a liquid crystal layerincluding a liquid crystal compound. In one embodiment, the liquidcrystal compound may be dispersed in the liquid crystal layer whilephase-separated from the aligned polymer network. The term “alignedpolymer network” used herein refers to a polymer network formed to aligna liquid crystal compound. The polymer network capable of aligning theliquid crystal compound may be formed by the following method. Theliquid crystal compound which can be dispersed in the aligned polymernetwork may be orientationally ordered by an action of the alignedpolymer network. In addition, an ordering direction of the liquidcrystal compound orientationally ordered in one direction may be changedby an external action. The term “external action” used herein refers toall kinds of actions performed to change ordering of the liquid crystalcompound, and a representative example thereof is the application of avoltage. The term “initial alignment or normal alignment” used hereinmay refer to an aligning or ordering direction of the liquid crystalcompound or an optical axis of a liquid crystal layer formed by theliquid crystal compound in a state in which the external action is notpresent. In addition, the term “initial or normal state” used herein mayrefer to a state of the liquid crystal device without the externalaction. In the liquid crystal device, an ordering direction of theliquid crystal compound in the initial alignment state may be changed byan external action, and when the external action disappears, the liquidcrystal compound may return to the initial alignment state.

The liquid crystal device may further include an alignment layer. Thealignment layer may be, for example, disposed adjacent to the liquidcrystal layer. The sentence “the alignment layer is disposed adjacent tothe liquid crystal layer” means that the alignment layer is disposed tohave an influence on the alignment of the liquid crystal layer, and inone embodiment, that the alignment layer is formed in contact with theliquid crystal layer. However, the alignment layer is not necessarilyplaced in contact with the liquid crystal layer as long as the alignmentlayer is placed to affect the alignment of the liquid crystal layer.FIG. 1 is a structure of an illustrative device, which includes analignment layer 101 and a liquid crystal layer 102 formed on one surfaceof the alignment layer 101. The liquid crystal layer 102 is an exampleof a liquid crystal device including a polymer network 1021 and a liquidcrystal region 1022. In FIG. 1, the alignment layer 101 is present onlyon one surface of the liquid crystal layer 102, but may be present onboth surfaces of the liquid crystal layer. In the specification, theliquid crystal region may refer to a region in which the liquid crystalcompound is present in the polymer network, and for example, as a regionincluding the liquid crystal compound, refer to a region in which theliquid crystal compound is dispersed in the network whilephase-separated from the polymer network. In FIG. 1, the liquid crystalcompound in the liquid crystal region 1022 may be indicated with anarrow.

The liquid crystal device may include a polarizing layer disposed on oneor both sides of the liquid crystal layer. As the polarizing layer,without particular limitation, a polarizing film formed of, for example,a conventional material used in a conventional LCD, such as poly(vinylalcohol) (PVA), or a polarizing layer embodied by a coating method suchas a polarization coating layer including a lyotropic liquid crystal(LLC), or a reactive mesogen (RM) and a dichroic dye. In thespecification, the polarizing layer embodied by a coating method may becalled a polarization coating layer. When the polarization coating layerincludes an LLC, the coating layer may further include a protectinglayer for protecting the LLC layer. As the LLC, without particularlimitation, a known liquid crystal may be used, and for example, an LLCcapable of forming an LLC layer having a dichroic ratio of 30 to 40 maybe used. Meanwhile, when the polarization coating layer includes an RMand a dichroic dye, a linear dye or a discotic dye may be used as adichroic dye. When the polarizing layer is present, arrangement of alight absorption axis may be selected in consideration of, for example,normal alignment of the liquid crystal layer and a mode of the device,but the preset invention is not particularly limited thereto. Forexample, to embody a normally white-mode device, two polarizing layersare placed on both sides of the liquid crystal layer. Here, lightabsorption axes of the polarizing layers may be placed at any one anglewithin 80 to 100 degrees, for example, perpendicular to each other. Inaddition, for example, to embody a normally black mode, two polarizinglayers are placed on both sides of the liquid crystal layer. Here, lightabsorption axes of polarizing layers may be disposed at any one anglewithin −10 to 10 degrees, for example, to be parallel to each other. Insuch a state, normal alignment of the liquid crystal layer may beaccomplished by placing light absorption axes of two polarizing layersat any one angle within 40 to 50 degrees, for example, at approximately45 degrees.

The liquid crystal device may include one or at least two base layers.Normally, the liquid crystal layer may be placed between the two baselayers opposite to each other. In such a structure, the alignment layermay be disposed on an inner side of the base layer, for example, betweenthe liquid crystal layer and the base layer. For example, the liquidcrystal device may further include base layers disposed opposite to eachother, and the liquid crystal layer may be present between the baselayers disposed opposite to each other. In some cases, the alignmentlayer may be present between the liquid crystal layer and the baselayer. FIG. 2 shows an illustrative liquid crystal device, which ispresent between base layers 201A and 201B spaced a predetermineddistance apart from each other and opposite to each other, and includesan alignment layer 101 and a liquid crystal layer 102. When the baselayer is present, the above-described polarizing layer may be normallypresent on an outer side of the base layer, but when needed, may bepresent on an inner side of the base layer, that is, between the liquidcrystal layer and the base layer. In such a case, as the polarizinglayer, it is preferable to use the above-described polarization coatinglayer.

As the base layer, a known material may be used without particularlimitation. For example, an inorganic film such as a glass film, acrystalline or non-crystalline silicon film, a quartz or indium tinoxide (ITO) film, or a plastic film may be used. As the base layer, anoptically isotropic base layer, an optically anisotropic base layer orpolarizing plate such as a retardation layer, or a color filtersubstrate may be used. For example, when the polarizing layer is presenton an inner side of the base layer, that is, between the liquid crystallayer and the base layer, although an anisotropic base layer is used asthe base layer, a device having a suitable performance can be embodied.

A plastic base layer may be, but is not limited to, a base layerincluding triacetyl cellulose (TAC); a cyclo olefin copolymer (COP) of anorbornene derivative; poly(methyl methacrylate (PMMA); polycarbonate(PC); polyethylene (PE); polypropylene (PP); polyvinyl alcohol (PVA);diacetyl cellulose (DAC); polyacrylate (Pac); poly ether sulfone (PES);polyetheretherketon (PEEK); polyphenylsulfone (PPS), polyetherimide(PEI); polyethylenemaphthatlate (PEN); polyethyleneterephtalate (PET);polyimide (PI); polysulfone (PSF); polyarylate (PAR), or an amorphousfluorine resin. In the base layer, as needed, a coating layer of asilicon compound such as gold, silver, silicon dioxide, or siliconmonoxide, a coating layer such as an anti-reflective layer may bepresent.

An electrode layer may be included on a surface of the base layer, forexample, a surface on the liquid crystal layer of the base layer (forexample, the alignment layer 101 of FIG. 2) or a surface of the baselayer 201A or 201B in contact with the liquid crystal layer 102. Theelectrode layer may be formed by depositing, for example, a conductivepolymer, a conductive metal, a conductive nanowire, or a metal oxidesuch as indium tin oxide (ITO). The electrode layer may be formed tohave transparency. In this field, various materials and methods forforming a transparent electrode layer are known, and all of thesemethods may be applied. When needed, the electrode layer formed on thesurface of the base layer may be suitably patterned.

A liquid crystal compound in the liquid crystal layer may be present ina normal state, for example, in a state in which the compound isorientationally ordered without an external action such as supply of avoltage, and such an ordering direction may be changed by an externalaction, for example, supply of an external voltage. Accordingly, in thepresent application, a device which can be exchanged between white andblack modes can be embodied. For example, the device of the presentapplication is a device embodied in a white mode without an externalaction (that is, in an initial state or a normal state), converted intoa black mode under an external action, and then converted into a whitemode when an external action is removed (such a device may normallyrefer to a white-mode device for convenience), or a device embodied in ablack mode without an external action (that is, an internal state or anormal state), converted into a white mode under an external action, andthen converted in a black mode when an external action is removed (sucha device may normally refer to a black-mode device for convenience). Forexample, as described above, a normally white-mode device can beembodied when a liquid crystal layer is normally disposed at any oneangle within 40 to 50 degrees, for example, at 45 degrees with a lightabsorption axis of the polarizing layer between two polarizing layerswhose light absorption axes are disposed at any one angle within 80 to100 degrees, for example, to be perpendicular to each other. In anotherexample, as described above, a normally black-mode device can beembodied when a liquid crystal layer is normally disposed at any oneangle within 40 to 50 degrees, for example, at 45 degrees, with a lightabsorption axis of the polarizing layer between two polarizing layerswhose light absorption axes are disposed at any one angle within −10 to10 degrees, for example, to be parallel to each other. In this state, ablack mode can be embodied by changing an alignment state of the liquidcrystal compound into, for example, a vertical alignment state by thesupply of a voltage. The term “black mode” used herein is a conceptdifferentiated from, so called, a dispersing mode, in a normal PDLC, andfor example, a haze in the black mode is 10% or less, 8% or less, 6% orless, or 5% or less. In addition, a haze in a white mode of the deviceof the present application is also 10% or less, 8% or less, 6% or less,or 5% or less. The haze may be a percentage of a transmittance ofdiffusion light with respect to a transmittance of entire transmissionlight penetrating a measuring target. The haze may be evaluated using ahazemeter (NDH-5000SP). The haze may be evaluated in the followingmethod using the hazemeter. That is, light is transmitted through themeasuring target, and incident into an integrating sphere. In thisprocess, light is separated into diffusion light (DT) and parallel light(PT) by the measuring target, and these lights are reflected in theintegrating sphere, and then collected in a light-receiving device. Thehaze can be measured through the collected light. That is, totaltransmission light (TT) obtained by the above process may be a sum(DT+PT) of the diffusion light (DT) and the parallel light (PT), and thehaze may be defined as a percentage (Haze (%)=100×DT/TT) of thediffusion light to the total transmission light. In addition, the liquidcrystal device of the present application may exhibit excellenttransparency in a transmission mode. For example, the liquid crystaldevice may exhibit light transmittance of 80% or more, 85% or more, 90%or more, or 95% or more without an external action in a normal alignmentstate, that is, a non-application of a voltage when the liquid crystaldevice is in a normal white mode. In addition, in a normal black mode,while an external action such as supply of a voltage is present, theabove-described light transmittance may be exhibited. The lighttransmittance may be a light transmittance with respect to any onewavelength in a visible region, for example, within approximately 400 to700 nm.

The liquid crystal device may have a high contrast ratio. The term“contrast ratio” used herein may refer to a rate (T/B) of a brightness(T) in the white mode and a brightness (B) in a black mode. In oneembodiment, the liquid crystal device includes the liquid crystal layer,and two polarizing layers, that is, first and second polarizing layers,disposed on both sides of the liquid crystal layer. The maximum value ofthe contrast ratio may be 200 or more, 250 or more, 300 or more, or 350or more. It means that the higher the contrast ratio is, the higherperformance the device has, and thus the upper limit of the contrastratio is not particularly limited. For example, the contrast ratio maybe 600, 550, 500, 450, or 400 or less. Such a contrast ratio may beperformed by embodying the device using the above-described alignedpolymer network and polarizing layer.

The liquid crystal device can be driven through low energy consumption,for example, a low driving voltage. For example, the liquid crystaldevice may have a voltage required to embody a 10% light transmittanceor 90% light transmittance of 30 V or lee, 25 V or less, or 20 V orless. That is, in the case of a normally white-mode device, a black modecan be embodied by changing an alignment direction of the liquid crystalcompound by the supply of a voltage, and in such a process, a voltagerequired to have a light transmittance of 10% may be in the above range.In contrast, in the case of the normally-black mode, a white mode can beembodied by changing an alignment direction of the liquid crystalcompound by the supply of a voltage, and in such a process, a voltagerequired to have a light transmittance of 90% may be in the above range.It means that the lower the voltage is, the higher performance thedevice has, and thus the lower limit of the required voltage is notparticularly limited. For example, the required voltage may be 5 V ormore. Such a low driving voltage may be obtained by embodying a deviceusing the above-described aligned polymer network and polarizing layer.

The liquid crystal layer of the liquid crystal device includes, apolymer network and a liquid crystal compound dispersed in the polymernetwork, and thus may have excellent thermal stability. For example, theliquid crystal layer may satisfy the following Equation A whenmaintained for 200 hours at 70° C. before and after thermal treatment.

|100×(X ₂ −X ₁)/X ₁|≦10%  [Equation A]

In Equation A, X₁ is a retardation of the liquid crystal layer beforethe thermal treatment, and X₂ is a retardation of the liquid crystallayer after the thermal treatment.

That is, the liquid crystal layer of the liquid crystal device may havean absolute value of a variation rate of the retardation before andafter the thermal treatment of 10% or less. As the absolute value ofsuch a variation rate is lower, the liquid crystal layer may have betterthermal stability, and the lower limit of the absolute value of thevariation rate is not particularly limited.

The polymer network may be a network of a precursor including, forexample, a polymerizable compound. Accordingly, the polymer network mayinclude the polymerizable compound in a polymerized state. As thepolymerizable compound, a non-liquid crystal compound that does not showcrystallinity may be used. When needed, as the polymerizable compound, aliquid crystal compound may be used, but in this case, a doublerefraction of the following polymer network may be considered.

For an alignment property of the polymer network, a composition of thepolymerizable compound forming the polymer network may be controlled.For example, the polymer network or the precursor may include at leastone of a bifunctional acrylate compound, a multifunctional, for example,tri- or more functional, acrylate compound and a monofunctional acrylatecompound. The polymer network may include the compound in a crosslinkedor polymerized state. The term “acrylate compound” used herein refers toa compound including an acryloyl group or a methacryloyl group, and thecompound including one functional group is a monofunctional acrylatecompound, and the compound including at least two functional groups is amultifunctional acrylate compound. For convenience of differentiation,hereinafter, the compound including two functional groups refer to abifunctional acrylate compound, and a multifunctional, for example, tri-or more functional, acrylate compound simply refers to a multifunctionalacrylate compound. The multifunctional acrylate compound may include,for example, 3 to 8, 3 to 7, 3 to 6, 3 to 5, or 3 to 4 functionalgroups.

To embody a suitable aligned polymer network, the polymer network or aprecursor thereof may include at least one compound of the bifunctional,multifunctional and monofunctional acrylate compounds to satisfyEquations 1 to 3.

A≧1.3×B  [Equation 1]

A≧C  [Equation 2]

A≧0.6×(B+C)  [Equation 3]

In Equations 1 to 3, A, B and C are weight ratios between the compoundscalculated by converting the sum of weights of the bifunctional acrylatecompound, the multifunctional acrylate compound and the monofunctionalacrylate compound, which are present in the precursor or polymernetwork, into 100. For example, when the precursor or polymer networkincludes only a bifunctional acrylate compound, in Equations 1 to 3, Ais 100, B and C are respectively 0. In another example, when theprecursor or polymer network only includes bifunctional andmonofunctional acrylate compounds, in Equations 1 to 3, each of A and Cis 50, and B is 0.

To ensure a suitable alignment property, for example, in Equation 1, avalue (A−1.3B) obtained by subtracting 1.3×B from A may be approximately0.5 to 100 or 1 to 100. In addition, to ensure a suitable alignmentproperty, for example, in Equation 2, a value (A−C) obtained bysubtracting C from A may be 0 to 100. In addition, to ensure a suitablealignment property, in Equation 3, a value (A−0.6(B+C)) obtained bysubtracting 0.6×(B+C) from A may be 2 to 100, 3 to 100, or 4 to 100.

To ensure a suitable alignment property, the polymer network or aprecursor thereof may include at least one compound of the bifunctional,multifunctional and monofunctional acrylate compounds to satisfyEquations 4 to 6.

A≧40  [Equation 4]

B≦30  [Equation 5]

C≦50  [Equation 6]

In Equations 4 to 6, A, B and C are as described in Equations 1 to 3.

In the above range, a suitable alignment property can be ensured in thepolymer network.

A kind of the acrylate compound included in the polymer network or aprecursor thereof is not particularly limited, and for example, any kindof the acrylate compound included in the polymer network or a precursorthereof, which can exhibit an aligning property within the rangesatisfying the above Equation, may not be used.

For example, as the bifunctional acrylate compound, a compoundrepresented by the Formula 1 may be used.

In Formula 1, R is each independently hydrogen or an alkyl group having1 to 4 carbon atoms, and X is an alkylene or alkylidene group having 1to 20 carbon atoms.

In addition, for example, as the multifunctional acrylate compound, acompound represented by Formula 2 may be used.

In Formula 2, n is a number of 3 or more, m is a number of 0 to 5, R iseach independently hydrogen or an alkyl group having 1 to 4 carbonatoms, X is a (m+n) valent radical, and Y is hydrogen or an alkyl group.

In addition, for example, as the monofunctional acrylate compound, acompound represented by Formula 3 may be used.

In Formula 3, R is hydrogen or an alkyl group having 1 to 4 carbonatoms, and Z is an alkyl group having 1 to 20 carbon atoms.

In Formulas 1 to 3, as an example of the alkyl group capable of beingpresent in R or Y, a methyl group or an ethyl group may be used.

In Formula 1, an alkylene group or alkylidene group of X may be, forexample, an alkylene or alkylidene group having 1 to 16, 1 to 12, 1 to10, 1 to 8, 2 to 8, or 4 to 8 carbon atoms. The alkylene or alkylidenegroup may be, for example, a linear, branched or cyclic type.

In Formula 2, n is any one of 3 or more, 3 to 8, 3 to 7, 3 to 6, 3 to 5,or 3 to 4. In addition, in Formula 2, m is any one of 0 to 5, 0 to 4, 0to 3, 0 to 2, or 0 to 1.

In Formulas 2, X is a (m+n) valent radical, for example, a hydrocarbonhaving 2 to 20, 2 to 16, 2 to 12, 2 to 8, or 2 to 6 carbon atoms, forexample, a (m+n) radical induced from a linear or branched alkane.

Meanwhile, in Formula 3, an alkyl group of X may be, for example, alinear or branched alkyl group having 1 to 20, 1 to 16, 1 to 12, 4 to12, or 6 to 12 carbon atoms.

A substituent defined by Formulas 1 to 3, for example, an alkyl group,an alkylene group, an alkylidene group, or a (m+n) valent radical may besubstituted by at least one substituent if needed, and as thesubstituent, for example, an alkyl group, an alkoxy group, an epoxygroup, an oxo group, an oxetanyl group, a thiol group, a cyano group, acarboxyl group or an aryl group may be used, but the present applicationis not limited thereto.

The polymer network or a precursor thereof may further include anadditive such as a solvent, a radical or cationic initiator capable ofinducing polymerization of the polymerizable liquid crystal compound, abasic material, a reactive compound capable of forming a network, or asurfactant, when further needed in the above-described compound.

The polymer network or precursor thereof may include a liquid crystalcompound, for example, a reactive liquid crystal compound. In such acase, a ratio of the liquid crystal compound is suitably controlled at asmall amount. In one embodiment, the polymer network may have a doublerefraction of 30 nm or less or 20 nm or less. That is, the polymernetwork may be an isotonic polymer network or a network having a doublerefraction within the above range. Thus, when the liquid crystalcompound is included, the polymer network may be included within a rangeexhibiting the above-described double refraction. The double refractionmay refer to an in-plane retardation calculated by Equation 6, or athickness-direction retardation calculated by Equation 7, and the lowerlimit may be 0 nm.

Rin=d×(nx−ny)  [Equation 6]

Rth=d×(nz−ny)  [Equation 7]

In Equations 6 and 7, Rin is an in-plane retardation, Rth is athickness-direction retardation, d is a thickness of the polymernetwork, nx is a refractive index in a slow axis direction on a surfaceof the polymer network, ny is a refractive index in a fast axisdirection on a surface of the polymer network, and nz is a refractiveindex of the polymer network in a thickness direction.

The polymer network and the liquid crystal compound in a liquid crystalregion may satisfy Equation B

(1−a)×{(2n _(o) ² +n _(e) ²)/3}^(0.5) ≦n _(p)≦(1+a)×n _(e)  [Equation B]

In Equation B, a is any one of 0 to 0.5, n_(o) is an ordinary refractiveindex of the liquid crystal compound, n_(e) is an extraordinaryrefractive index of the liquid crystal compound, and n_(p) is arefractive index of the polymer network.

The term “refractive index, retardation or double refraction” usedherein may be, unless particularly defined otherwise, a refractiveindex, retardation or double refraction measured with respect to lighthaving a wavelength of 550 nm. In addition, when the ordinary refractiveindex of the polymer network is different from an extraordinaryrefractive index thereof, the term “refractive index of the polymernetwork” refers to an ordinary refractive index of the network. As thepolymer network and the liquid crystal compound are selected to satisfyEquation B, a device exhibiting excellent transparency and ensuring ahigh contrast ratio in a white mode can be provided.

In Equation B, a may be, for example, less than 0.4, 0.3, 0.2, or 0.1,or 0.

The polymer network may have a dielectric anisotropy of 3 or more, 3.5or more, or 4 or more. In such a range of the dielectric anisotropy, adriving voltage property of the liquid crystal device may be excellentlymaintained. The upper limit of the dielectric anisotropy may be, but isnot particularly limited to, approximately 20 or less, 15 or less, or 10or less.

A liquid crystal region dispersed in the polymer network includes aliquid crystal compound. As the liquid crystal compound, all kinds ofcompounds which are phase-separated in the polymer network, and alignedby the polymer network. For example, as the liquid crystal compound, asmectic liquid crystal compound, a nematic liquid crystal compound, or acholesteric liquid crystal compound may be used. The liquid crystalcompound may be phase-separated, may not be bound with the polymernetwork, and may be changed in an aligning property under an externalaction such as an external voltage. To this end, for example, the liquidcrystal compound may be a compound without having a polymerizable groupor crosslinking group.

In one embodiment, as the liquid crystal compound, a nematic liquidcrystal compound may be used. As the compound, for example, as theliquid crystal compound satisfying Equation C, for example, a nematicliquid crystal compound may be used.

(n _(e) +n _(o))/2−b≦{(2n _(o) ² +n _(e) ²)/3}^(0.5)≦(n _(e) +n_(o))/2+b  [Equation C]

In Equation C, n_(e) is an extraordinary refractive index of the liquidcrystal compound, n₀ is an ordinary refractive index of the liquidcrystal compound, and b is any one of 0.1 to 1.

As a liquid crystal compound satisfying Equation B is selected, a deviceexhibiting excellent transparency and ensuring high contrast ratio in awhite mode can be provided.

In Equation 2, in another example, b is 0.1 to 0.9, 0.1 to 0.7, 0.1 to0.5, or 0.1 to 0.3.

The liquid crystal compound may have a difference between anextraordinary dielectric anisotropy (∈_(e), dielectric anisotropy in alonger axis direction) and an ordinary dielectric anisotropy (∈_(o),dielectric anisotropy in a shorter axis direction) of 4 or more, 6 ormore, 8 or more, or 10 or more. As the difference in dielectricanisotropy is higher, the device can exhibit suitable characteristics,and the upper limit is not particularly limited. For example, as theliquid crystal compound, a compound having an extraordinary dielectricanisotropy (∈_(e), dielectric anisotropy in a longer axis direction) ofapproximately 6 to 50, and an ordinary dielectric anisotropy (∈_(o),dielectric anisotropy in a shorter axis direction) of approximately 2.5to 7.

A liquid crystal layer or the following polymerizable composition mayinclude 5 to 50 parts by weight of the polymer network (or the followingpolymer network precursor) and 50 to 95 parts by weight of the liquidcrystal compound. In another example, the liquid crystal layer or thefollowing polymerizable composition may include 5 to 45 parts by weightof the polymer network (or the following polymer network precursor) and55 to 95 parts by weight of the liquid crystal compound, 5 to 40 partsby weight of the polymer network (or the following polymer networkprecursor) and 60 to 95 parts by weight of the liquid crystal compound,5 to 35 parts by weight of the polymer network (or the following polymernetwork precursor) and 65 to 95 parts by weight of the liquid crystalcompound, 5 to 30 parts by weight of the polymer network (or thefollowing polymer network precursor) and 70 to 95 parts by weight of theliquid crystal compound, 5 to 25 parts by weight of the polymer network(or the following polymer network precursor) and 75 to 95 parts byweight of the liquid crystal compound, 20 to 50 parts by weight of thepolymer network (or the following polymer network precursor) and 80 to95 parts by weight of the liquid crystal compound, or 5 to 15 parts byweight of the polymer network (or the following polymer networkprecursor) and 85 to 95 parts by weight of the liquid crystal compound.The term “pars by weight” used herein may refer to a weight ratiobetween components. Within such a range of the weight ratio, thealigning property of the polymer network may be suitably maintained.

A retardation (Rc) of the liquid crystal layer may be determined by amode or structure of the device, but the present application is notparticularly limited thereto. For example, the liquid crystal layer mayhave a retardation with respect to a wavelength of 550 nm ofapproximately 240 nm to 310 nm, 245 nm to 305 nm, or 250 nm to 300 nm.Such a range of the retardation may be suitable to embody, for example,a normally white-mode device between two polarizing layers.

The liquid crystal layer may satisfy, for example, the followingEquation D.

247 nm≦{d×(n _(e) −n _(o))}×A≦302 nm  [Equation D]

In Equation D, d is a thickness (unit: nm) of the liquid crystal layer,n_(e) is an extraordinary refractive index of the liquid crystalcompound, n_(o) is an ordinary refractive index of the liquid crystalcompound, and A is a ratio (L/T) of a weight (L) of the liquid crystalcompound to a total weight (T) of the polymer network and the liquidcrystal compound, or a ratio (VL/TV) of a volume (VL) of the liquidcrystal compound to a total volume (TV) of the liquid crystal layer.

In Equation D, the value calculated by {d×(n_(e)−n_(o))}×A is atheoretical retardation of the liquid crystal layer. The theoreticalretardation of the liquid crystal layer is suitable to approach aretardation (measured retardation) of the above-described liquid crystallayer. For example, in Equation D, an absolute value of a differencebetween the value calculated by {d×(n_(e)−n_(o))}×A and the measuredretardation of the liquid crystal layer may be approximately 15 nm orless, 10 nm or less, 8 nm or less, or 5 nm or less. The liquid crystallayer satisfying Equation D may be suitable to embody, for example, anormally white-mode device between two polarizing layers.

In Equation D, (n_(e)−n_(o)) may be, for example, 0.05 to 0.20. Inanother example, the (n_(e)−n_(o)) may be 0.07 or more. In still anotherexample, the (n_(e)−n_(o)) may be 0118 or less or 0.15 or less.

In Equation D, A is A is a ratio (L/T) of a weight (L) of the liquidcrystal compound toa total weight (T) of the polymer network and theliquid crystal compound, or a ratio (VL/TV) of a volume (VL) of theliquid crystal compound to a total volume (TV) of the liquid crystallayer, which may be within 0.5 to 0.98. The ratio (L/T or VL/TV) may be,in another example, 0.6 or more or 0.7 or more.

A thickness of the liquid crystal layer is not particularly limited aslong as it is set to satisfy the above description, and may be, forexample, within approximately 1 μm to 10 μm.

When the liquid crystal device includes an alignment layer, as thealignment layer, for example, an alignment layer including aphoto-alignment compound may be used. The term “photo-alignmentcompound” used herein may refer to a compound orientationally orderedthrough radiation of light, and capable of aligning an adjacent liquidcrystal compound in a predetermined direction through an interactionsuch as anisotropic interaction in the ordered state. In the alignmentlayer, the photo-alignment compound may be ordered to have orientation.The photo-alignment compound may be a unimolecular compound, a monomericcompound, an oligomeric compound, or a polymeric compound.

A photo-alignment compound may be a compound including a photosensitivemoiety. Various photo-alignment compounds capable of being used inalignment of the liquid crystal compound are known. As thephoto-alignment compound, for example, a compound ordered by trans-cisphotoisomerization; a compound ordered by photo-destruction such aschain scission or photo-oxidation; a compound ordered byphotocrosslinking or photopolymerization such as [2+2] cycloaddition,[4+4] cycloaddition or photodimerization; a compound ordered byphoto-Fries rearrangement; or a compound ordered by ringopening/closure. As the compound ordered by trans-cisphotoisomerization, for example, an azo compound such as a sulfonateddiazo dye or an azo polymer, or a stilbenes may be used, and as thecompound ordered by photo-destruction,cyclobutane-1,2,3,4-tetracarboxylic dianhydride, aromatic polysilane orpolyester, polystyrene or polyimide may be used. In addition, as thecompound ordered by photocros slinking or photopolymerization, acinnamate compound, a coumarin compound, a cinnamamide compound, atetrahydrophthalimide compound, a maleimide compound, a benzophenonecompound or a diphenylacetylene compound or a compound having achalconyl residue as a photosensitive residue (hereinafter, a chalconcompound) or a compound having an anthracenyl residue (hereinafter, ananthracenyl compound) may be used, as the compound ordered byphoto-Fries rearrangement, an aromatic compound such as a benzoatecompound, a benzoamide compound or a methacrylamidoaryl methacrylatecompound may be used, and as the compound ordered by ringopening/closure, a compound ordered by ring opening/closure of a [4+2]i-electronic system such as a spiropyran compound may be used, but thepresent application is not limited thereto.

The photo-alignment compound may be a unimolecular compound, a monomericcompound, an oligomeric compound or a polymeric compound, or a blend ofthe photo-alignment compound and a polymer. Here, the oligomeric orpolymeric compound may have a moiety induced from the photo-alignmentcompound or the photosensitive moiety at a main or side chain.

As the polymer having a moiety induced from the photo-alignment compoundor the photosensitive moiety, and mixed with the photo-alignmentcompound, polynorbornene, polyolefin, polyarylate, polyacrylate,poly(meth)acrylate, polyimide, poly(amic acid), polymaleimide,polyacrylamide, polymethacrylamide, polyvinylether, polyvinylester,polystyrene, polysiloxane, polyacrylnitrile or polymethacrylnitrile maybe used, but the present application is not limited thereto.

The polymer included in the alignment compound may be, but is notlimited to, representatively, polynorbornene cinnamate, polynorbornenealkoxy cinnamate, polynorbornene allyloyloxy cinnamate, polynorbornenefluorinated cinnamate, polynorbornene chlorinated cinnamate orpolynorbornene dicinnamate.

When the alignment compound is a polymeric compound, the compound mayhave, but is not limited to, for example, a number average molecularweight of approximately 10,000 to 500,000 g/mol.

The alignment layer may be formed by, for example, blending a requiredadditive such as a photoinitiator to the photo-aligned compound to coat,and radiating polarizing UV in a desired direction.

Another aspect of the present application provides a polymerizablecomposition. For example, the polymerizable composition may be used toform a liquid crystal layer of the above-described liquid crystaldevice. That is, the polymerizable composition may be a precursorcomposition of the liquid crystal layer.

For example, the polymerizable composition may include a precursor of analigned polymer network including at least one of a bifunctionalacrylate compound, a multifunctional, for example, tri- or morefunctional, acrylate compound, and a monofunctional acrylate compound tosatisfy Equations 1 to 3, if necessary, Equations 1 to 6 and a liquidcrystal compound.

In addition, for example, the polymerizable composition may include 50to 95 parts by weight of the precursor of the aligned polymer networkincluding at least one of a bifunctional acrylate compound, amultifunctional, for example, tri- or more functional, acrylatecompound, and a monofunctional acrylate compound and 5 to 50 parts byweight of the liquid crystal compound.

The illustrative polymerizable composition may include a precursor and aliquid crystal compound of an aligned polymer network. The precursor maybe composed to form, for example, the above-described aligned polymernetwork. The precursor may include a polymerizable compound, forexample, the bifunctional, multifunctional and/or monofunctionalacrylate compound. The precursor may include the acrylate compound in aratio satisfying the above-described Equations 1 to 6, and a kind ordielectric anisotropy of another acrylate compound, and the thingsrelating to Equation B may also be applied in the same manner A kind ofthe liquid crystal compound included in the precursor is notparticularly limited, either, and the above descriptions including, forexample, the things relating to Equation C may be applied. In addition,the above description on the ratio of the precursor and the liquidcrystal compound may also be applied in the same manner.

The polymerizable composition may include a ball-shaped spacer in asuitable ratio to maintain the formed liquid crystal layer at a suitabledistance, when needed. The shape and size of the spacer are notparticularly limited, and may be selected to ensure a desired distanceof the liquid crystal layer. The ratio of the spacer is not particularlylimited, and may be included, for example, at approximately 0.1 wt % to5 wt % in the total polymerizable composition.

The polymerizable composition may be prepared by dissolving an additive(for example, an initiator) additionally required to the precursor andthe liquid crystal compound in a suitable solvent. As the solvent, knownsolvents such as toluene, xylene, cyclopentanone and cyclohexanone canbe used.

In one embodiment, the polymerizable composition may be composed in asolventless type. The solvent-type polymerizable composition ispreferable to be applied to the following squeeze coating method. Amethod of manufacturing the solventless type poylmerizable compositionis not particularly limited, and may control viscosities or ratios ofother components without using the solvent which is included in theabove-described composition.

Still another aspect of the present application provides a method ofmanufacturing a liquid crystal device. The manufacturing method mayinclude forming a liquid crystal layer including a liquid crystalcompound dispersed in a polymer network by polymerizing a layer formedby coating a polymerizable composition. Here, as the polymerizablecomposition, for example, a precursor composition of the above-describedliquid crystal layer may be used. Here, the polymerization may beperformed by radiating suitable energy, for example, light, capable ofinducing polymerization.

A method of forming the layer including the polymerizable compositionmay be a known coating method such as roll coating, printing, inkjetcoating, slit nozzling, bar coating, comma coating, spin coating orgravure coating without particular limitation. In one embodiment, thelayer including the polymerizable composition may be formed by a squeezecoating method. To apply a squeeze coating method, the above-describedsolventless-type composition may be used as the polymerizablecomposition. Through the application of a squeeze coating method, a moreuniform liquid crystal layer can be formed, and the liquid crystal layercan be directly laminated with a base layer without a separate adhesivelayer, which may be preferable for driving voltage.

In the squeeze coating method, the layer including the polymerizablecomposition may be formed by placing the polymerizable compositionbetween two base layers, for example, between the above-described baselayer, and applying a pressure to at least one of the base layer. Here,a method of applying the pressure may use a pressure roller withoutparticular limitation. The application of the pressure may be performedsimultaneously or sequentially to the entire surface of the base layer.FIG. 3 is a diagram showing the squeeze coating method. As shown in FIG.3, first, a polymerizable composition 301, for example, theabove-described solventless-type composition is placed on apredetermined part of a base layer 201A, and then a base layer 201B isplaced thereon. Subsequently, a pressure roller 302 is placed on atleast one of the base layers to sequentially press the base layer.Though not shown in FIG. 3, the above-described electrode layer and/oralignment layer may be disposed on an inner side of the base layers 201Aand 201B, for example, on a side finally in contact with the liquidcrystal layer. In the squeeze coating method, polymerization may beperformed simultaneously with the pressing process, or performed afterthe pressing process.

To form a suitable aligned polymer network, the polymerization may beperformed on the alignment layer. For example, the liquid crystal layermay be formed by forming the layer including the polymerizablecomposition, or forming the layer between two alignment layers oppositeto each other and applying energy to polymerize.

The alignment layer may include, for example, a photo-aligned compoundsuch as the above-described photo-aligned compound. Such an alignmentlayer may be formed by coating a precursor of the alignment layer on asuitable substrate, for example, the base layer, exposing the coatedlayer, and aligning the photo-aligned compound. FIG. 4 schematicallyshows a process of forming an alignment layer 101 by radiating light tothe precursor of the alignment layer formed on a base layer 201A.

The precursor of the alignment layer may further include, for example,an initiator to the photo-aligned compound at an appropriate amount, andmay also include another additive such as a surfactant when needed. Thelayer of the precursor of the alignment layer may be formed by coatingthe precursor by a conventional coating method such as bar coating,comma coating, inkjet coating or spin coating. For example, theabove-described transparent electrode layer may be formed on a surfaceof the base layer on which the precursor layer is formed.

After the precursor layer is formed, energy may be applied by radiatinglight to the layer. The radiation of light may be performed after asolvent is volatilized by drying the formed layer under a suitablecondition when the precursor includes a solvent. The drying may beperformed, for example, for approximately 1 to 5 minutes atapproximately 60 to 130° C., but the present application is not limitedthereto.

The radiation of light may be performed to order the alignment compoundincluding the precursor layer. Normally, the ordering of the alignmentcompound may be performed using linearly-polarized light. The wavelengthor intensity of the radiated light may be selected to suitably order thealignment compound. The ordered photo-aligned compound is ordered bylight in a visible or near-ultraviolet range, but when needed, light ina far-ultraviolet or near-infrared range may be used.

A layer including a polymerizable composition may be formed to beadjacent to the alignment layer by the above-described squeeze coatingmethod after the alignment layer is formed. FIG. 5 schematically shows aprocess of forming a liquid crystal layer 102 by radiating light to alayer including a polymerizable composition present on a surface of thealignment layer 101 shown in FIG. 4. FIG. 5 shows that a liquid crystallayer is formed on one alignment layer, but when needed, the liquidcrystal layer may be formed between two alignment layers as describedabove.

A polymer network and a liquid crystal region may be formed throughpolymerization of a polymer network precursor and phase separation of aliquid crystal compound according to the above-described process.

To form a suitable alignment network, the polymerization may beperformed while the precursor layer for the liquid crystal layer, thatis, the above-described layer including the polymerizable composition ismaintained in a liquid crystal phase, for example, a nematic phase. Whenthe layer is formed in a non-nematic state, for example, an isotropicphase, a suitable alignment property may not be ensured. To maintain thenematic phase, the polymerization may be performed at a temperature lessthan a nematic temperature (Tni) of the precursor layer for the liquidcrystal layer, that is, the layer including the polymerizablecomposition. The term “nematic temperature” used herein refers to atemperature at which the layer is changed into an isotropic state from anematic state, and the range of the temperature may be determinedaccording to the composition of the layer. As long as the polymerizationis performed at less than the nematic temperature of the layer, that is,while the layer is in a nematic state, the temperature is notparticularly limited thereto.

Conditions for the application of energy for polymerization, forexample, the radiation of light, are not particularly limited, as longas a polymer network is formed by polymerizing the polymerizablecompound, and the liquid crystal compound is phase-separated to form theliquid crystal region. When needed, to further stimulate the formationof the polymer network, application of suitable heat or exposure may beperformed before or after the radiation of light, or at the same time.

After the liquid crystal layer is formed through the above process, whenneeded, a process of disposing a polarizing layer on one or both sidesof the liquid crystal layer may be further performed. For example, afterthe liquid crystal layer is formed, a process for disposing thepolarizing layer on both sides of the liquid crystal layer such thatlight absorption axes have any one angle from 80 to 100 degrees, forexample, are perpendicular to each other, or such that light absorptionaxes have any one angle from −10 to 10 degrees, for example, areparallel to each other may be further performed.

Yet another aspect of the present application provides a system formanufacturing a liquid crystal device, for example, the above-describedliquid crystal device.

The manufacturing system may include a polymerization inducing meansinstalled to provide energy capable of inducing polymerization of aprecursor of the liquid crystal layer, for example, the above-describedpolymerizable composition. Here, detailed descriptions on a polymernetwork precursor included in the precursor of the liquid crystal layerand a liquid crystal compound may be the same as described above.

A kind of the polymerization inducing means is not particularly limited,and a heating or light radiating means may be used to apply or radiateenergy such as heat or light to the precursor may be used.

The manufacturing system may also include a loading means installed tomaintain the precursor layer for the liquid crystal layer. The liquidcrystal layer can be formed through polymerization while the precursorlayer is maintained by such a loading means.

A kind of the loading means is not particularly limited as long as itcan load the precursor of the liquid crystal layer. For example, theloading means may be installed to maintain a surface of the precursorlayer to be curved at least in the polymerization of the precursor ofthe liquid crystal layer. An example of such a loading means may be aroll.

That is, in one embodiment, the manufacturing system is, so called, aroll-to-roll manufacturing system, which includes at least one guideroll formed to transfer the precursor layer for the liquid crystallayer. Due to the guide roll, the layer can be transferred, andsequentially a liquid crystal device can be manufactured. In addition,the polymerization may progress on the guide roll while the surface ofthe layer is maintained in a curved form, and in this case, the guideroll may serve as the loading means. A more uniform liquid crystal layercan be formed by performing the polymerization while the surface of theliquid crystal layer is maintained in a curved form by theabove-described guide roll. The roll-to-roll system may further include,for example, an unwinding roll releasing the layer or a base layer onwhich the layer will be formed and introducing towards thepolymerization inducing means, or a winding roll winding the liquidcrystal device whose manufacturing process such as polymerization isdone to recover.

The manufacturing device may include a temperature control meansinstalled to maintain a temperature to allot the polymerizable compoundto be maintained in a liquid crystal phase like the above-describednematic phase at least during the polymerization, that is, while thepolymerizable compound is polymerized.

The temperature control means is not particularly limited as long as itcan be formed to maintain a suitable temperature, and may be composedof, for example, a temperature control drum and/or an inert gas purgingchamber.

For example, if the manufacturing system is the above-describedroll-to-roll system, as a temperature control drum, for example, acooling drum, is included in the guide roll also capable of serving asthe loading means to maintain a temperature in a suitable range duringthe polymerization. When needed, the system may be composed to beincluded in the inert gas purging chamber such as a region in whichpolymerization occurs while loaded to such a guide roll, and to includea polymerization inducing means in the purging chamber.

FIG. 6 is an illustrative diagram showing a predetermined part of themanufacturing system embodied as described above. The system includes aguide roll A including a temperature control means such as a coolingdrum; and an inert gas purging chamber B installed to introduce theprecursor layer C for the liquid crystal layer transferred by the guideroll A. In FIG. 6, the system includes the guide roll A including atemperature control means and having a chamber B, but may omit any oneof the above two components as long as it maintains a suitabletemperature. In such a configuration, a polymerization inducing means,for example, a UV lamp as show in FIG. 6, installed to apply energy ontothe precursor layer transferred by the guide roll A may be furtherincluded, and may be present, for example, in the chamber B.

In the manufacturing device, specific kinds of other means except theabove-described components are not particularly limited. For example, inthe corresponding field, various methods embodying the roll-to-rollsystem are known, and such a method may be applied to the system bysuitably being changed when needed.

For example, the roll-to-roll system may be configured to recover aproduct finally manufactured through a process of sequentially formingan electrode layer, an alignment layer, a layer including apolymerizable composition (for example, the layer of the polymerizablecomposition may be formed by the squeeze coating method) andpolymerizing the layer, and a process of laminating or forming apolarizing layer when needed by a recovering means such as a windingroll.

Yet another aspect of the present application provides relates to a useof the liquid crystal device. The illustrative liquid crystal device maybe simply and continuously manufactured through, for example, aroll-to-roll process. The liquid crystal device may also be embodied asa flexible device, and ensure an excellent contrast ratio.

For example, the present application relates to an optical modulatorincluding the liquid crystal device. As the optical modulator, a smartwindow, a window protecting film, a flexible display device, an activeretarder for displaying 3D images or a viewing angle control film may beused, but the present application is not limited thereto. A method ofconfiguring such an optical modulator is not particularly limited, and aconventional method may be applied as long as the liquid crystal deviceis used.

Effect

A liquid crystal device of the present application is a device capableof exhibiting a normally white mode or normally black mode, driven witha low driving voltage by exhibiting a high contrast ratio, andexhibiting excellent durability such as thermal stability. Such a liquidcrystal device can be applied to various optical modulators such as asmart window, a window protecting film, a flexible display device, anactive retarder for a 3D image display or a viewing angle control film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 show an illustrative liquid crystal device.

FIGS. 3 and 5 are diagrams illustrating a process of manufacturing theillustrative device.

FIG. 6 is a diagram showing a system for manufacturing the illustrativeliquid crystal device.

FIGS. 7 to 17 show evaluation results for the liquid crystal device inExamples and Comparative Examples.

EXPLANATION OF THE MARKS IN THE DRAWINGS

-   -   101: the alignment layer    -   102: the liquid crystal layer    -   1021: the polymer network    -   1022: the liquid crystal region    -   201A, 201B: base layers    -   301: the polymerizable composition    -   302: the pressure roller

Illustrative Embodiments

Hereinafter, the above will be described in more detail by Examples andComparative Examples; however the scope of the above is not limited tothe below.

Example 1 Formation of Alignment Layer

A precursor of an alignment layer was prepared by dissolving a mixtureof polynorbornene (PNBCi, molecular weight (Mw): 85,000, polydispersityindex (PDI): approximately 4.75) including the repeating unit of FormulaA and a photoinitiator (Irgacure 907) as an alignment compound in atoluene solvent to have a solid content of the polynorbornene of 2 wt %.An alignment layer was formed by coating the precursor of the alignmentlayer on a transparent electrode layer of a polycarbonate (PC) film onwhich an indium tin oxide (ITO) transparent electrode layer is formed,and applying linearly-polarized UV rays (1,200 mJ/cm²) by means of awire grid polarizer (WGP).

Manufacture of Liquid Crystal Device

A precursor of a liquid crystal layer (polymerizable composition;nematic temperature (Tni): approximately 50° C.) was prepared by mixing1.6-hexanediol diacrylate as a polymer network precursor with a liquidcrystal compound (Merck, MAT-12-529, ne: 1.6092, no: 1.4820) in a weightratio (polymer network precursor:liquid crystal compound) of 1:9, anddissolving the mixture in toluene with a suitable amount of aninitiator. Afterward, the precursor of the liquid crystal layer wascoated on a surface of the manufacture alignment layer to have athickness of a final liquid crystal layer of 2.5 μm. A liquid crystallayer was formed by stacking a surface of the alignment layer of the PCfilm on one surface of which the alignment layer was formed to be incontact with the coating layer on the coated precursor of the liquidcrystal layer, and polymerizing a polymer network precursor by radiatingUV rays (300 mW/cm²). A temperature during the UV radiation wasmaintained at approximately 25° C., and thus the precursor of the liquidcrystal layer was maintained in a nematic phase. A refractive index of apolymer network for forming the liquid crystal layer measured with aprism coupler was approximately 1.456, and a phase retardation (measuredretardation) of the liquid crystal layer measured using Axostep(Axometrics) equipment according to the manual of a manufacturer basedon a wavelength of 550 nm was approximately 288 nm FIG. 7 is an opticalmicroscope image of the liquid crystal layer, and FIG. 8 is a scanningelectron microscope (SEM) image of the liquid crystal layer.

Example 2

A liquid crystal layer was formed by the same method as described inExample 1, except that a mixture of 50 parts by weight of 1,6-hexanedioldiacrylate and 50 parts by weight of 2-ethylhexyl acrylate was used as apolymer network precursor. Here, a nematic temperature (Tni) of theprecursor of the liquid crystal layer was approximately 45° C., and theUV radiation was performed at a temperature maintaining the precursor ina nematic phase, for example, 25° C. A refractive index of the polymernetwork in the formed liquid crystal layer was approximately 1.446, andthe measured retardation of the liquid crystal layer was approximately286.7 mm.

Example 3

A liquid crystal layer was formed by the same method as described inExample 1, except that a mixture of 40 parts by weight of 1,6-hexanedioldiacrylate, 20 parts by weight of trimethylolpropane triacrylate and 40parts by weight of 2-ethylhexyl acrylate was used as a polymer networkprecursor. Here, a nematic temperature (Tni) of the precursor of theliquid crystal layer was approximately 45° C., and the UV radiation wasperformed at a temperature maintaining the precursor in a nematic phase,for example, 25° C. A refractive index of the polymer network in theformed liquid crystal layer was approximately 1.452, and the measuredretardation of the liquid crystal layer was approximately 285.3 mm.

Example 4

A liquid crystal layer was formed by the same method as described inExample 1, except that a mixture of 40 parts by weight of 1,6-hexanedioldiacrylate, 30 parts by weight of trimethylolpropane triacrylate and 30parts by weight of 2-ethylhexyl acrylate was used as a polymer networkprecursor. Here, a nematic temperature (Tni) of the precursor of theliquid crystal layer was approximately 50° C., and the UV radiation wasperformed at a temperature maintaining the precursor in a nematic phase,for example, 25° C. A refractive index of the polymer network in theformed liquid crystal layer was approximately 1.455, and the measuredretardation of the liquid crystal layer was approximately 286.1 mm.

Example 5

A liquid crystal layer was formed by the same method as described inExample 1, except that a mixture of 70 parts by weight of 1,6-hexanedioldiacrylate and 30 parts by weight of trimethylolpropane triacrylate wasused as a polymer network precursor. Here, a nematic temperature (Tni)of the precursor of the liquid crystal layer was approximately 50° C.,and the UV radiation was performed at a temperature maintaining theprecursor in a nematic phase, for example, 25° C. A refractive index ofthe polymer network in the formed liquid crystal layer was approximately1.461, and the measured retardation of the liquid crystal layer wasapproximately 287 mm.

Comparative Example 1

A liquid crystal layer was formed by the same method as described inExample 1, except that a mixture of 40 parts by weight of 1,6-hexanedioldiacrylate, and 60 parts by weight of 2-ethylhexyl acrylate was used asa polymer network precursor, and the polymer network precursor and theliquid crystal compound were mixed in a weight ratio (polymer networkprecursor:liquid crystal compound) of 10:90. Here, a nematic temperature(Tni) of the precursor of the liquid crystal layer was approximately 45°C., and the UV radiation was performed at a temperature maintaining theprecursor in a nematic phase, for example, 25° C. A refractive index ofthe polymer network in the formed liquid crystal layer was approximately1.444, and the measured retardation of the liquid crystal layer wasapproximately 124 mm.

Comparative Example 2

A liquid crystal layer was formed by the same method as described inExample 1, except that a mixture of 30 parts by weight of 1,6-hexanedioldiacrylate, 20 parts by weight of trimethylolpropane triacrylate and 50parts by weight of 2-ethylhexyl acrylate was used as a polymer networkprecursor, and the polymer network precursor and the liquid crystalcompound were mixed in a weight ratio (polymer network precursor:liquidcrystal compound) of 10:90. Here, a nematic temperature (Tni) of theprecursor of the liquid crystal layer was approximately 45° C., and theUV radiation was performed at a temperature maintaining the precursor ina nematic phase, for example, 25° C. A refractive index of the polymernetwork in the formed liquid crystal layer was approximately 1.450, andthe measured retardation of the liquid crystal layer was approximately162 mm.

Comparative Example 3

A liquid crystal layer was formed by the same method as described inExample 1, except that a mixture of 30 parts by weight of 1,6-hexanedioldiacrylate, 40 parts by weight of trimethylolpropane triacrylate and 30parts by weight of 2-ethylhexyl acrylate was used as a polymer networkprecursor, and the polymer network precursor and the liquid crystalcompound were mixed in a weight ratio (polymer network precursor:liquidcrystal compound) of 10:90. Here, a nematic temperature (Tni) of theprecursor of the liquid crystal layer was approximately 45° C., and theUV radiation was performed at a temperature maintaining the precursor ina nematic phase, for example, 25° C. A refractive index of the polymernetwork in the formed liquid crystal layer was approximately 1.457, andthe measured retardation of the liquid crystal layer was approximately166 mm.

Comparative Example 4

A liquid crystal layer was formed by the same method as described inExample 1, except that a mixture of 40 parts by weight of 1,6-hexanedioldiacrylate, 40 parts by weight of trimethylolpropane triacrylate and 20parts by weight of 2-ethylhexyl acrylate was used as a polymer networkprecursor, and the polymer network precursor and the liquid crystalcompound were mixed in a weight ratio (polymer network precursor:liquidcrystal compound) of 10:90. Here, a nematic temperature (Tni) of theprecursor of the liquid crystal layer was approximately 50° C., and theUV radiation was performed at a temperature maintaining the precursor ina nematic phase, for example, 25° C. A refractive index of the polymernetwork in the formed liquid crystal layer was approximately 1.459, andthe measured retardation of the liquid crystal layer was approximately157 mm.

Comparative Example 5

A liquid crystal layer was formed by the same method as described inExample 1, except that a mixture of 60 parts by weight of 1,6-hexanedioldiacrylate and 40 parts by weight of trimethylolpropane triacrylate wasused as a polymer network precursor, and the polymer network precursorand the liquid crystal compound were mixed in a weight ratio (polymernetwork precursor:liquid crystal compound) of 10:90. Here, a nematictemperature (Tni) of the precursor of the liquid crystal layer wasapproximately 50° C., and the UV radiation was performed at atemperature maintaining the precursor in a nematic phase, for example,25° C. A refractive index of the polymer network in the formed liquidcrystal layer was approximately 1.463 and the measured retardation ofthe liquid crystal layer was approximately 182 mm.

Comparative Example 6

A liquid crystal layer was formed by the same method as described inExample 1, except that only a liquid crystal compound was injectedbetween PC films having an alignment layer to form a liquid crystallayer without using a polymer network precursor. Here, a measuredretardation of the liquid crystal layer was approximately 319 nm.

Comparative Example 7

A liquid crystal layer switched between a dispersing mode and atransparent mode was formed by forming a liquid crystal layer having athickness of approximately 25 μm between two PC films not having analignment layer using a precursor of a liquid crystal layer prepared bymixing 40 parts by weight of a polymer network precursor (PN-393, Merck)and 60 parts by weight of a liquid crystal compound as a precursorcapable of forming a device switched between a dispersing mode and atransparent mode. A haze in the dispersing mode of the layer crystallayer formed as described above was approximately 92.91%, and aretardation thereof was approximately 65 nm.

Comparative Example 8

A liquid crystal layer was formed by the same method as described inExample 1, except that a precursor of a liquid crystal layer prepared bymixing 10 parts by weight of a reactive liquid crystal compound and 90parts by weight of a liquid crystal compound using a reactive liquidcrystal compound (RM257, Merck) as a polymer network precursor was used.Here, a nematic temperature of the precursor of the liquid crystal layerwas approximately 85° C., and the UV radiation was performed at atemperature maintaining the precursor in a nematic phase, for example,25° C.

Comparative Example 9

A liquid crystal layer was formed by the same method as described inExample 1, except that a mixture of 20 parts by weight of 1,6-hexanedioldiacrylate and 80 parts by weight of a liquid crystal compound was usedas a polymer network precursor. Here, a nematic temperature (Tni) of theprecursor of the liquid crystal layer was approximately 10° C., and theUV radiation was performed at a temperature in which the precursor wasmaintained in an isotropic phase, for example, 25° C. A retardation(measured retardation) of the liquid crystal layer measured usingAxostep (Axometrics) equipment according to the manual of a manufacturerbased on a wavelength of 550 nm was approximately 139 nm.

Comparative Example 10

A liquid crystal layer was formed by the same method as described inExample 1, except that UV radiation was performed at a temperature inwhich a precursor of a liquid crystal layer was maintained in anisotropic phase, for example, 60° C. Here, a refractive index of apolymer network in the manufactured liquid crystal layer measured usinga prism coupler was approximately 1.456, and a retardation (measuredretardation) of the liquid crystal layer measured using Axostep(Axometrics) equipment according to the manual of a manufacturer basedon a wavelength of 550 nm was approximately 88 nm. FIG. 18 shows data ofthe liquid crystal layer, which was measured by Axostep.

Comparative Example 11

A liquid crystal layer was formed by the same method as described inExample 1, except that a PC film not having a photo-alignment layer wasused. Here, a refractive index of a polymer network in the manufacturedliquid crystal layer measured using a prism coupler was approximately1.456, and a retardation (measured retardation) of the liquid crystallayer measured using Axostep (Axometrics) equipment according to themanual of a manufacturer based on a wavelength of 550 nm wasapproximately 46 nm. FIG. 18 shows data of the liquid crystal layer,which was measured by Axostep.

Comparative Example 12

A liquid crystal layer was formed by the same method as described inExample 1, except that a precursor of a liquid crystal layer wasprepared by blending a polymer network precursor and a liquid crystalcompound in a weight ratio (polymer network precursor:liquid crystalcompound) of 4:6. A retardation (measured retardation) of the liquidcrystal layer measured using Axostep (Axometrics) equipment according tothe manual of a manufacturer based on a wavelength of 550 nm wasapproximately 139 nm.

Experimental Example 1 Evaluation of Alignment Property of PolymerNetwork

The liquid crystal layer manufactured in Example was placed between twopolarizing plates disposed such that light absorption axes wereperpendicular to each other or between two polarizing plates in whichlight absorption axes were disposed at 45 degrees, and an alignmentproperty was evaluated by confirming whether the liquid crystal layerwas switched between a white mode and a black mode while revolving. Whenthe liquid crystal layer was switched between the white and black modesthrough the above-described process, it was evaluated that a liquidcrystal compound was aligned in the liquid crystal layer due to thealignment property of a polymer network. According to the evaluationresults, in Examples 1 to 5, switching between the white and black modeswas confirmed, but in Comparative Examples 1 to 5 and ComparativeExamples 9 to 12, polymer networks did not exhibit alignment properties.FIG. 9 shows evaluation results with respect to Comparative Examples 1to 5, and FIG. 10 shows evaluation results with respect to ComparativeExamples 1 to 5. In addition, FIG. 16 is a diagram showing thecomparison between Example 1 and Comparative Example 9, and in Example 1in which the formation of the liquid crystal layer was performed in anematic phase of a precursor as confirmed from the drawings, a whitemode (left) was exhibited when the liquid crystal layer was disposed at45 degrees with a polarization axis, and a black mode (right) wasexhibited when the liquid crystal layer was disposed at 90 degrees witha polarization axis. However, in Comparative Example 9 in which theformation of a liquid crystal layer was performed in a state in which aprecursor was in an isotropic state, it was seen that switching betweenthe white and black modes was impossible since light was blocked at bothstates in which the liquid crystal layer was disposed at 45 and 90degrees (left and right) with a polarization axis.

Experimental Example 2 Evaluation of Retardation, Haze and Transmittanceof Liquid Crystal Layer

The retardation, haze and transmittance of the liquid crystal layersmanufactured in Examples 1 to 5 were evaluated. Here, the retardation(measurement wavelength: 550 nm) was measured according to the manual ofa manufacturer based on a wavelength of 550 nm using Axostep(Axometrics) equipment, and the haze and transmittance were alsomeasured according to the manual of a manufacturer using a hazemeter(NDH-5000SP). Here, the retardation was evaluated in a state in which avoltage was not applied to the liquid crystal layer, and the haze andtransmittance were evaluated by applying a driving voltage. FIG. 11 is adiagram showing results obtained by evaluating retardations with respectto Examples, and FIG. 12 is a diagram showing results obtained byevaluating haze and transmittance with respect to Examples. FIG. 15shows AXO-STEP measured data for Example 1 and Comparative Example 1.

Experimental Example 3

A contrast ratio was evaluated by evaluating a brightness by applying avoltage to the liquid crystal layers manufactured in Examples andComparative Examples step by step. The brightness and contrast ratiowere evaluated by converting values measured by LCMS-200 equipment(Sesim Photonics Technology). In the evaluation process, a distancebetween a measurement target and a light receiving part (detector) wasmaintained at approximately 10 cm, and a diameter of the light receivingpart (detector) was approximately 1.5 mm FIG. 13 shows evaluationresults for Example 1, and Comparative Examples 1 and 7. For evaluation,the liquid crystal layers of Example 1 and Comparative Example 1 wereplaced between two polarizing plates in which light absorption axes wereperpendicular to each other, and in the case of Comparative Example 7configured to be switched between a dispersing mode and a white(transmitting) mode, a contrast ratio between the dispersing mode andthe white (transmitting) mode was evaluated without using a polarizingplate. As seen from the drawings, in Example 1, the maximum contrastratio was 350 or more, in Comparative Examples 1 and 7, the contrastratio was 100 or less. Meanwhile, the maximum contrast ratios inExamples 2 to 5 were all 350 or more, and the maximum contrast ratios inComparative Examples 2 to 6, 8 and 9 were all less than 100.

Experimental Example 4

In Examples 1 and 7, a transmittance according to a driving voltage wasevaluated. In Example 1, the device exhibiting a normally white mode wasconfigured by disposing the liquid crystal layer between two polarizingplates in which light absorption axes were perpendicular to each otherto be aligned at 45 degrees with the light absorption axis of thepolarizing plate, and then the transmittance was evaluated by applying avoltage and switching a black mode, and in Comparative Example 7, adriving voltage was measured by applying a voltage to the device presentin a normally dispersing mode to be converted into a white mode. FIG. 14shows the measurement results, and as seen from FIG. 14, in Example 1, adriving voltage for exhibiting a transmittance of 10% was 16.5 V, and inComparative Example 7, a driving voltage for exhibiting a transmittanceof 90% was 92.4 V. Meanwhile, as the evaluation was performed in thesame manner in Examples 2 to 5, the driving voltages for exhibiting atransmittance of 10% were all less than 30 V, in Comparative Examples 1to 6, 8 and 9, the driving voltages for exhibiting a transmittance of10% were all 90V or more.

Experimental Example 5 Evaluation of Thermal Stability

Thermal stabilities of the liquid crystal layer (measured retardation:288 nm) manufactured in Example 1 and the liquid crystal layer (measuredretardation: 319 nm) manufactured in Comparative Example 6 wereevaluated. Specifically, the thermal stability was evaluated byevaluating a retardation after each liquid crystal layer was maintainedin an oven at 70° C. for 200 hours. Afterward, in Example 1, the minimumand maximum retardations were 254.4 nm and 278.9 nm, respectively, theaverage retardation was 263 nm, and a retardation change was 8.7%. InComparative Example 6, the minimum and maximum retardations were 226.2nm and 273.9 nm, respectively, the average retardation was 254.2 nm, aretardation change was 20.4%. In addition, as the result of evaluatingthermal stabilities of Examples 2 to 5 in the same manner, theretardation changes were all less than 10%.

What is claimed is:
 1. A liquid crystal device, comprising: a liquidcrystal layer comprising an alignable polymer network and a liquidcrystal compound orientationally ordered according to one direction inthe polymer network; and first and second polarizing layers which aredisposed on both sides of the liquid crystal layer, and of which lightabsorption axes form an angle within the range from 80 degrees to 100degrees or from −10 degrees to 10 degrees, an initial ordering directionof the liquid crystal compound forming an angle within the range from 40degrees to 50 degrees with the light absorption axis of the polarizinglayer.
 2. The liquid crystal device according to claim 1, wherein theordering direction of the liquid crystal compound is switchable by anexternal action, and wherein the device is configured to beinterchangeable between a light transmission mode and a light blockingmode according to the change of the ordering direction.
 3. The liquidcrystal device according to claim 2, wherein hazes in the lighttransmission mode and the light blocking mode are 10% or less.
 4. Theliquid crystal device according to claim 1, wherein a retardation of theliquid crystal layer with respect to 550 nm is in the range from 240 nmto 310 nm in a state where the liquid crystal compound is orderedaccording to the initial ordering direction.
 5. The liquid crystaldevice according to claim 1, satisfying the Equation D below:247 nm≦{d×(n _(e) −n _(o))}×A≦302 nm  [Equation D] wherein the “d” is athickness (unit: nm) of the liquid crystal layer, the “n_(e)” is anextraordinary refractive index of the liquid crystal compound, the“n_(o)” is an ordinary refractive index of the liquid crystal compound,and the “A” is a ratio (L/T) of a weight (L) of the liquid crystalcompound with respect to a total weight (T) of the polymer network andthe liquid crystal compound; or a ratio (VL/TV) of a volume (VL) of theliquid crystal compound with respect to a total volume (TV) of theliquid crystal layer.
 6. The liquid crystal device according to claim 5,wherein a value obtained by subtracting the ordinary refractive index ofthe liquid crystal compound from the extraordinary refractive index ofthe liquid crystal compound is in the range from 0.05 to 0.20.
 7. Theliquid crystal device according to claim 5, wherein the ratio (L/T) ofthe weight (L) of the liquid crystal compound with respect to the totalweight (T) of the polymer network and the liquid crystal compound; orthe ratio (VL/TV) of a volume (VL) of the liquid crystal compound withrespect to the total volume (TV) of the liquid crystal layer is in therange from 0.5 to 0.98.
 8. The liquid crystal device according to claim5, wherein the thickness of the liquid crystal layer is in the rangefrom 1 μm to 10 μm.
 9. The liquid crystal device according to claim 1,further comprising base layers which are disposed so as to face eachother, wherein the liquid crystal layer is between the base layers, andthe polarizing layer is between the base layer and the liquid crystallayer.
 10. The liquid crystal device according to claim 9, wherein thepolarizing layer is a polarization coating layer comprising orderedlyotropic liquid crystals.
 11. The liquid crystal device according toclaim 10, wherein the polarizing layer further comprises a protectinglayer protecting the ordered lyotropic liquid crystals.
 12. The liquidcrystal device according to claim 11, wherein a dichroic ratio of thepolarizing layer is in the range from 30 to
 40. 13. The liquid crystaldevice according to claim 1, wherein the polarizing layer is apolarization coating layer comprising an ordered reactive mesogencompound and a dichroic dye.
 14. The liquid crystal device according toclaim 13, wherein the dichroic dye has a linear or discotic structure.15. The liquid crystal device according to claim 1, further comprising:an alignment layer disposed adjacent to the liquid crystal layer. 16.The liquid crystal device according to claim 1, wherein the polymernetwork is a network of a precursor comprising at least one selectedfrom a group consisting of a bifunctional acrylate compound, amultifunctional that is tri or more functional acrylate compound and amonofunctional acrylate compound such that they can satisfy theEquations 1 to 3 below:A≧1.3×B  [Equation 1]A≧C  [Equation 2]A≧0.6×(B+C)  [Equation 3] wherein the “A,” “B” and “C” are weight ratiosbetween the compounds calculated when the sum of weights of thebifunctional acrylate compound, the multifunctional and themonofunctional acrylate compound in the precursor are converted into100.
 17. The liquid crystal device according to claim 16, wherein theprecursor comprises at least one selected from a group consisting of thebifunctional acrylate compound, the multifunctional acrylate compoundand the monofunctional acrylate compound such that they further satisfythe Equations 4 to 6 below:A≧40  [Equation 4]B≦30  [Equation 5]C≦50,  [Equation 6] wherein the “A,” “B” and “C” are weight ratiosbetween the compounds calculated when the sum of weights of thebifunctional acrylate compound, the multifunctional and themonofunctional acrylate compound in the precursor are converted into100.
 18. An optical modulator comprising the liquid crystal device ofclaim 1.